1. Field of the Invention
The present invention relates to a projector which projects an image to a screen.
2. Description of the Related Art
Projectors are utilized as means for a plurality of people to simultaneously share video information at, for example, small planning sessions, meetings, large conferences and seminars. That is, the projector is portable and enables all participants to simultaneously view the same material and understand its content. Thus, the projector serves in achieving efficient meetings and sessions or convincing presentations.
Since projectors have not heretofore been light enough to carry with ease, they have only been moved between rooms in the same building and have lacked portability. However, electronic devices have recently been reduced in size and weight along with, for example, development in integrated technology of the electronic devices, so that portable projectors are also being realized owing to the size reduction.
For example, US 2002/0024637 A1 proposes a projector in which a digital micromirror device (DMD: a registered trademark of Texas Instruments, Inc., of the United States) is used as a light modulating device.
Herein, the DMD is a device in which a reflective surface is configured by a plurality of square micromirrors arranged in a matrix. Each micromirror has a diagonal pivot shaft, that is a pivot shaft with an inclination of 45 degrees with respect to an arranging direction of the mirror, and is configured to change its direction depending on whether it is turned on or off. In other words, if illumination light and reflected light are arranged to enter/exit along a plane which is perpendicular to the pivot shaft of the micromirror, the reflected light is emitted in a different direction depending on whether the mirror is turned off (off position) or on (on position). Thus, a projection lens is disposed, for example, in a direction in which the reflected light is projected when the mirror is turned on such that the reflected light can be projected on a screen. Therefore, each of the micromirrors of such a DMD is adapted to correspond to a pixel, and each micromirror is turned on/off in accordance with a value of each pixel of an input image, thereby making it possible to configure a projector which projects an image corresponding to the input image.
The projector disclosed in US 2002/0024637 A1 described above has the following configuration. Light emitted from a light source is led to an optical system for illumination via an integrator rod. The light emitted from the optical system for illumination has its light path bent by a total internal reflection (TIR) prism, and enters, as the illumination light, the DMD disposed on a DMD substrate. The reflected light (ON light) reflected by the DMD passes through the TIR prism and is projected to the screen by an optical system for projection.
It is to be noted that because the pivot shaft of each mirror of the DMD has an inclination of 45 degrees with respect to the arranging direction of the mirror as described above, the illumination light of the DMD needs to enter from a direction having an inclination of 45 degrees with respect to the arranging direction of the mirror of the DMD. Therefore, in the projector disclosed in US 2002/0024637 A1 described above, the DMD is mounted on the DMD substrate at an inclination of 45 degrees. The reason that the optical system for illumination which emits the illumination light are not inclined but the DMD is inclined as described above is to enable the projector to be stored in a small thin case. However, if the DMD is disposed with an inclination of 45 degrees as described above, the image projected to the screen is inclined at 45 degrees. Thus, in US 2002/0024637 A1 described above, a projection unit storing such a configuration is mounted on a projector base so that it can pivot 45 degrees on a rotation hinge around a shaft vertical to the DMD. In other words, during projection, the projection unit is inclined at 45 degrees so that an erect projection image is projected on the screen.
Furthermore, US 2002/0180939 A1 discloses a projector having the following configuration of an optical system. That is, light emitted from a light source is condensed to an integrator rod via a color wheel. The light emitted from the integrator rod is led to a TIR prism by a plurality of mirrors, and is totally reflected by the TIR prism to illuminate the DMD. Thus, the DMD is illuminated from a required direction with a required incidence angle. The illumination light thus illuminating is then reflected by the DMD to perform light modulation. The light which has passed through the TIR prism after the light modulation is projected to a screen by an optical system for projection.
Thus, the optical system for illumination uses a plurality of mirrors so that normal projection can be performed without disposing the DMD with inclination.